We present a consistent theory of N = 1 supergravity in twelvedimensions with the signature (10, 2). Even though the formulation uses two null vectors violating the manifest Lorentz covariance, all the superspace Bianchi identities are satisfied. After a simple dimensional reduction to ten-dimensions, this theory reproduces the N = 1 supergravity in tendimensions, supporting the consistency of the system. We also show that our supergravity can be the consistent backgrounds for heterotic or type-I superstring in Green-Schwarz formulation, by confirming the fermionic κ -invariance of the total action. This theory is supposed to be the purely N = 1 supergravity sector for the field theory limit of the recently predicted F-theory in twelve-dimensions.